This invention relates generally to efficient vaporization of cryogenic fluids, and more particularly to control of flow of ambient air acting to transfer heat to the cryogenic fluid, with control of air discharge as a function of incident wind direction.
Ambient air vaporizers have been used to convert cryogenic liquids into warm gas for over fifty years. To move the ambient air across the heat transfer surfaces, many rely on the natural draft effect. The cryogenic fluids being warmed (vaporized) are passed adjacent vertical heat transfer surfaces while being heated; and the ambient air descends at the other sides of such surfaces. The change in the density of the air as it cools induces a draft (the opposite of a chimney). The velocity of the induced draft is a function of the change in density. At the outlet (bottom) of the vaporizer, the cooled air typically turns to flow horizontally. For a single operating unit, this will cause discharge of the air in a 360° horizontal fan. In large vaporizer arrays, such as large industrial gas users (steel mills) or LNG re-gasification terminals, the exits may be confined to a single directional axis. As long as sufficient height is provided underneath the vaporizer, as by the vaporizer unit legs, this works well. However, in the event of adverse winds, the static pressure generated by the wind is sufficient to slow or even stop the induced draft, thus curtailing the desired vaporization. With high enough winds, the flow may even reverse, disturbing the temperature profile of adjacent vaporizers.